Method of forming an article

ABSTRACT

A method of making an article includes determining the greatest dimension of an article along a selected axis, and manufacturing a first part of the article between an end and a face lying in the laterally extending plane containing the dimension. The method further includes placing the article on the support of direct layer deposition (DLD) apparatus with the face upwards, and forming the remaining part of the article using the DLD apparatus.

BACKGROUND AND SUMMARY

This invention relates to a method of forming an article.

The laser sintering/melting of powdered materials to form solid parts isnow well known, though the forming of nominally 100% dense metal partsby a practical process is relatively new.

In particular there are commercial powder bed ‘Selective LaserSintering’/‘Selective Laser Melting’ (SLS/SLM) machines such as the M270produced by Electron Optical Systems (EOS) M270 and the Realizer IImarketed by MCP. These take metal powders under an inert atmosphere anddirect a CO₂ or fibre laser onto a layer of powder.

There are other similar powder bed machines and somewhat relatedprocesses such as ‘Direct Laser Fabrication’ (blown powder). Genericallya point source of energy such as a laser or electron beam is selectivelyapplied to a layer of powder and a 3D part built up layer wise from a‘slicing’ of a design file. The heat from the point source melts orsinters the particulates to form a solid that may be further processedto fully solidify or render useful by various means not relevant to thisdisclosure.

The term Direct Layer Deposition (DLD) can be used to describe all suchprocesses and we will here describe only the powder bed SLS/SLM process.In the powder bed systems, powder is fused at a single plane and theobject thus built is formed from a cycle of selectively sintered/meltedpowder at the upper surface of the powder bed, stepping the powder bedand part built object down by one layer and recoating powder across thesurface of the bed and part-built object. This way objects are built upin layers and the built part is surrounded by the powder bed. Extremelyaccurate building is possible with good surface finishes.

Powders are typically 10's to 100's of microns in size and the layersare typically 10's to 100's of microns thick.

The point source of energy penetrates into the surface to a depthgreater than the nominal layer thickness and typically to a depth of1˜1.5 times a layer thickness such that if 20 micron layers are beingbuild, the penetration of the energy source is 20 to 30 microns. This isclearly visible from a micrograph of a cross section of a built part andevidences that energy penetrates into the previously built surfacecausing fusion of the previously built surface to the new powderapplied.

Support structures are required (as is familiar to those skilled in thisart) for certain geometries and structures. Broadly, any surface that isat less than approximately 30 degrees from horizontal will require asupport. These supports provide a ‘foundation’ upon which melted powdercan wet and solidify (rather than simply balling up as ‘splatter’)and/or provides mechanical tethering to keep geometric accuracy of thestructure as it is built particularly as thermal stress may be createdby the build process.

By their very nature these supports are not part of the desired geometryand therefore need to be designed, built and removed. This is both timeconsuming and requires skill thereby adding delay and cost.

A further problem is that the geometry of the part may be such that itis difficult or impossible to locate support structures that can beremoved—thereby limiting the geometries that can be made by the DLDprocess.

Two or more parts may be joined together e.g. in a welding process wherea point source of energy and materials is applied to the place ofconjoining. It is also known to ‘build up’ material by e.g. welding andthen further work this deposited material by e.g. filing, cutting ormachining such that a repair can be effected upon a part that is brokenor damaged.

Whilst useful this process is time consuming and the second part made bywelding is not (near) net shape and subsequent working such as cuttingand gauging is required.

It is also known to mould a second material onto inserts but in thesecases the mechanical linkage of the two parts and the building method ofthe second part are different. There are therefore 3 layers and twointerfaces in this system being the two parts and the bonding system andthereby it is more prone to failure. Typically the insert is of a highertemperature material as the moulding temperature must not damage ordistort the insert. Also there are geometric limits to mouldingprocesses and materials limitations dictated by the moulding process.

It is known to clad one material to a part by applying a powder of thesecond material to the first part and applying e.g. heat and/or pressureto fuse the second material and the first to the second.

Hot Isostatic Pressure (HIP) of powdered material to build net shapeparts or to join parts is known. HiPing is also known to create asurface layer of at least 0.2 mm of one material upon a blank made ofanother material e.g. see U.S. Pat. No. 6,015,627 where an aluminiumdrum is placed in a HiPing can and hard powdered material is HIPed ontothe surface to form a ‘blank’ which is then removed from the can andforged into a magnetic head drum for use in helical scan magneticrecording apparatus.

From one aspect the invention consists in a method of making an articleincluding:

(a) determining the greatest dimension of an article along a selectedaxis;

(b) manufacturing a first part of the article between an end and a facelying in the laterally extending plane containing the dimension;

(c) placing the article on the support of direct layer deposition (DLD)apparatus with the face upwards; and

(d) forming the remaining part of the article using the DLD apparatus.

The part may be clamped to the support.

The DLD apparatus may be either a selective layer sintering apparatus ora selective laser melt apparatus.

It is particularly preferred that the step (d) joins the formingremaining part to the first part.

The parts may be of different materials.

From another aspect the invention is a method (or any object made bysuch a method) of making complex solid objects by joining an alreadybuilt part to a further part by using the same method for joining as tobuild that further part.

Either method may include the application of a point source of energysuch as a laser or electron beam that can both soften or melt thesurface of the already built part and also the materials used to buildthe further part to form the object. It is understood that the recipe ofthe method may have variations through time such as applied power,pressure, dwell time and build depth whilst still being the same method.

In particular the method to build the further part is a selectivelayering process where material is added e.g. by the application ofmaterial and a point source of energy to cause it to fuse together.

More particularly the invention is the process of making an object by acontiguous joining and net shape or near net shape building process ofone part such as by a powder bed SLS/SLM process to an already builtpart of that object.

It should be understood that the materials of the two parts may be thesame or different and in particular the material of the second part mayhave a higher melting point that the material of the first part. Forexample the first part may be of a Stainless Steel and the second partCobalt Chrome or other high temperature alloy such as a Nickel superalloy.

To clarify, the co-joined parts are not made by a single, interruptedbut otherwise continuous process and in particular the invention is inobjects that cannot be made by a single (perhaps interrupted) process. Amechanical translation and/or materials change or the like is carriedbetween the two processes.

The invention is also any solid object wherein the object is in at leasttwo co-joined parts wherein at least one part is net shape or near netshape and the joining is contiguous with that one part and not the otherpart.

This is counter intuitive for two reasons. In this invention the joiningis contiguous with the forming of the second part. It is expected tocommence with already formed parts and bring them together to be joined(e.g. by welding) or to create a mass of second material upon a firstpart e.g. by welding and then subsequently form the second part e.g.through cutting, filing and the like.

Further, the powder bed process is considered a method a building asingle part to replace assemblies, so it is not obvious to turn it intoa joining process. So the invention may be seen as a method of using aselective layer deposition process to join two parts together.

For example the invention enables a complex part to be built with apre-built part as foundation for a powder bed SLS/SLM process and inparticular a part (preferably but not necessarily made by a powder bedprocess) is located such that a powder bed process can commence at asurface of the already built part. This requirement includes thepre-part is located;

a) Firmly, to avoid intolerable movement induced by the thermal stressof the SLS/SLM process,

b) Vertically, with a powder source aligned with respect to the layerheight to be built upon the building surface of the pre-built part, inparticular the upper surface of a powder bed (e.g. within about 4 timesthe diameter of the average particulate size),

c) Laterally such that the building process (induced by the energysource) and the pre-built part are correctly aligned with respect toeach other.

A method of achieving this is to form an attachment part for the firstpart at the same time as the first part and by the same means as thefirst part whereby the first part, once removed can be relocated andclamped to this attachment part to provide accurate location during thebuilding of the second part.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described by reference to the figures, in which:

FIG. 1 shows chronological stages a˜d of a prior art process of formingan article;

FIG. 2 shows chronological stages a˜d of a process of forming an articleaccording to the present invention; and

FIGS. 3 and 4 depict articles formed according to the present invention.

Diagrams a˜d of FIGS. 1 and 2 chronologically show stages of the buildprocess and do not represent physical stopping of the process nor anymeaningful intermediate stages.

DETAILED DESCRIPTION

FIGS. 1 a and b show intermediate stages of the powder bed SLS/SLMprocess. The start point is a base plate 1 and powder 4. A thin layer ofpowder is placed by various means familiar to those familiar with thesemachines across the base plate—e.g. by pushing powder from a powdersource bin with a re-coater blade 8. A point source of energy 6 such asa laser beam is directed at the powder causing it to fuse to form asolid 2 being part of a desired 3 dimensional solid object. The baseplate is indexed downwards and a fresh layer of powder created acrossthe base plate and the solid 2 in build. The ambient 5 is an inert gassuch as argon or is de-oxygenated air. Typically the base plate 2 iswarmed to above ambient to enable easy thermal control. At 3 a supportstructure is being built. This is not a desired part of the solid objectbut is required by a subsequent part of the building process. Suchsupports can be custom designed or generated automatically by “Magics”software from Materialise, Leuven, Belgium.

At FIG. 1.b is a later intermediate step immediately prior to thecommencement of the building of 2 a, a part of the solid 2 shown at FIG.1.c. This part 2 a is impossible to build without support 3 beneath it.If the point source of energy 6 is directed at the powder bed 4 then thepowder simply fuses into discrete lumps. The support 3 provides asurface for wetting and to provide mechanical stability and enable acontinuous build of part 2 a and 2.

At FIG. 1.d is shown the completed solid 2 in powder bed 4.

In this simplistic example it can still be seen that removal of support3 is non trivial and time consuming. It should be appreciated that thereare practical real-world examples where supports are required insideobjects or in other hard to reach places rendering the object eithercostly or unmanufacturable by this otherwise suitable process.

In FIG. 2 is shown the invention. The intention is to make the sameobject 2 as in FIG. 1, without the requirement for supports. Thestarting point is to commence the build of the solid object 2 at thecommencement of 2 a such that the base plate 1 provides the function ofsupport 3. This building continues until at FIG. 2.a the intermediatesolid object 2 i has been completed being the object 2 missing thoselevels of the build in the same plane as the previously required supportstructure 3.

The intermediate solid object 2 i is now removed from the base plate 1e.g. by wire Electro Discharge Machine or saw, inverted and placed backon the base plate as shown at FIG. 2 b and located with respect to thepoint source of energy 6 by e.g. clamps 7. The upper level is alsoaligned with the upper surface of the powder bed 4 e.g. by adding powderuntil the bed is level with the top of 2 i.

The building process continues until the object 2 is completed as shownat FIG. 2 c. It can then be released from the base plate by undoing theclamps 7.

As can be appreciated there may be additional heat treatments and stressrelieving steps without affecting the generality of the invention.

Further, intermediate object 2 i may be made from a different materialor indeed by a different process and could for example by a machined,forged or cast part. By such means a multi-material construct may beformed without discrete joining processes.

FIGS. 3 and 4 shows an object made by the method of the invention Thecompleted object was made in two different EOS M270 powder bed laser‘sintering’ (melting) machines from stainless steel and cobalt chromepowder. In FIG. 4 the completed object can be seen as removed from thesecond M270 clamped by removable clamps to an attachment part formed ona base plate. In the foreground can be seen where the object waspartially formed in the first M270 in stainless steel on that base platebefore being removed and reattached by the clamps to the attachmentpart. After clamping the partially built object was placed back into thesecond EOS M270 and the upper ‘horn’ of the object was formed in cobaltchrome. This required the partially built stainless steel object to beburied in the cobalt chrome powder until its upper surface was alignedwith the top of the powder bed.

1. A method of making an article including: (a) determining the greatestdimension of an article along a selected axis; (b) manufacturing a firstpart of the article between an end and a face lying in the laterallyextending plane containing the dimension; (c) placing the article on thesupport of direct layer deposition (DLD) apparatus with the faceupwards; and (d) forming the remaining part of the article using the DLDapparatus.
 2. A method as claimed in claim 1, wherein the part isclamped to the support.
 3. A method as claimed in claim 1 wherein theDLD apparatus is by either a selective laser sintering apparatus or aselective laser melt apparatus.
 4. A method as claimed in claim 2wherein the DLD apparatus is by either a selective laser sinteringapparatus or a selective laser melt.
 5. A method as claimed in claim 1,wherein the step (d) joins the forming remaining part to the first part.6. A method as claimed in claim 2 wherein the step (d) joins theremaining part to the first part.
 7. A method as claimed in claim 1,wherein the parts are of different materials.
 8. A method of making acomplex object by joining an already built part to a further part byusing the same method for joining as to build that further part.
 9. Amethod as claimed in claim 8 where the further part is made by DirectLaser Deposition
 10. A method as claimed in claim 9 where the DirectLaser Deposition method is a selective laser sintering or meltingmethod.
 11. A method as claimed in claim 1 where the material melted orsintered is a metal or metal alloy.
 12. A method as claimed in claim 11where the material of either or both the already built and further partsis a high temperature metal or alloy such as titanium or a ‘super alloy’such as cobalt chrome or a nickel or nickel/iron based alloy.
 13. Amethod as claimed in claim 1 wherein an attachment part for the firstpart is formed at the same time and by the same means as the first partwhereby the first part, once removed can be relocated and clamped tothis attachment part to provide accurate location during the building ofthe second part.
 14. A method as claimed in claim 8 wherein anattachment part for the first part is formed at the same time and by thesame means as the first part whereby the first part, once removed can berelocated and clamped to this attachment part to provide accuratelocation during the building of the second part.